1. Field of the Invention
This invention relates to exposure control systems for cameras, and more particularly to an exposure control system for a camera of the type provided with shutter preselection and diaphragm preselection automatic exposure ranges and with a manual exposure range. Still more particularly, it relates to a switching arrangement for selectively establishing one of three possible combinations of channels for transmiting photographic analog information between exposure control parameter setting means and exposure determining means either directly or through a computer circuit when the manual or automatic exposure range is operative respectively.
2. Description of the Prior Art
In a prior art camera of the type described when switched in the shutter preselection automatic exposure range, the shutter dial of the camera is manually operated to set into an exposure control circuit a desired shutter time in the form of an analog signal. The latter is combined by a computer, i.e. a computing device, with additional analog signals supplied from a film speed setter and a light value sensor to produce an output representative of an effective exposure aperture. This is applied to a diaphragm value indicator and which is utilized in controlling the operation of a diaphragm control. In the case of the diaphragm preselection automatic exposure range, a diaphragm ring is manually operated to set into the exposure control circuit a desired diaphragm value in the form of an analog signal. The computing device is combined with additional analog signals supplied from the film speed setter and the light value sensor to produce an output representative of an effective shutter time. The latter is applied to a shutter time indicator and is utilized in controlling operation of a shutter control. In the case of the manual exposure range, the shutter dial and diaphragm ring are manually adjusted, whereby the shutter means is controlled electrically, while the diaphragm means is set in position mechanically.
Widely accepted cameras are of the type having a single automatic exposure range, that is, either a shutter preselection automatic exposure range alone, or a diaphragm preselection automatic exposure range alone these are provided with a device which permits the photographer, who is looking through the view-finder of the camera, to view the preselected shutter time or diaphragm aperture value as well as the pointer of an electronic exposure meter in or near the image field of the finder with the use of supplementary optical means such as prisms. A scale plate may be arranged in the finder and operatively linked with either the shutter dial, or the diaphragm ring. Most of prior art cameras of the type provided with the shutter preselection and diaphragm preselection automatic exposure ranges other than digitally controlled cameras of the same type are adapted to display the result of computation for an exposure value alone, which can be seen, upon looking into the finder. In the field of view of the finder, The provision for displaying the preselected shutter time or diaphragm aperture value in the field of view of the finder is not be made in the finder of the camera to avoid an increase in the complexity of the camera structure. Digitally controlled cameras in which photographic information is digitally processed are generally provided with digital display devices for displaying the preselected shutter time and/or diaphragm aperture values or value as well as an exposure value as the result of digital computation. However they have the disadvantage of increasing the complexity of the structures of the camera and production cost thereof because of the necessity of an analog-to-digital converter for converting the output of the light value sensor which produces an analog output signal in response to the level of brightness of an object being photographed. A digital device does however have the advantage of satisfying the need for highly accurate automatic exposure control over an extended range of light levels.
In addition to the above mentioned disadvantages of the dual range type camera has another disadvantage that the mechanism for switching the camera between the two automatic exposure ranges is associated with circuit-transfer switching means for two circuit arrangements one of which is operative in the shutter preselection exposure range, and the other in the diaphragm preselection exposure range. The switching mechanism is more complicated in structure than that employed in the single range type of cameras. This results in an increase in the possibility of malfunction of the exposure control circuit.
A further disadvantage is that the construction, arrangement and form of the switching mechanism with the circuittransfer switching means must be specially manufactured for incorporation in the camera. It must take into account the fact that the electrical conducting characteristics of the switching means are very sensitive to the formation of oxide films and deposition of dusts effected between the working members thereof, or otherwise the accuracy and reliability in aperture or shutter time control could not be stabilized with increase in the number of operations. This is so because the exposure control circuit is designed to operate with little electrical power on the order of microwatts from a miniature mercury cell or silver cell. Such a special switching mechanism is not amenable to low unit cost production techniques.
Recently, a new problem has arisen, because a rapidly everincreasing proportion of the total camera production, from first class cameras of simple construction up to super-high class cameras with systematized components therefor, have been manufactured with electronic controls. Most of these controls employ integrated circuits as the essential parts of the light value sensor, computer and switching circuit controlling operation of the shutter or diaphragm means. On the other hand, most of the camera makers have so far individually produced a wide variety of cameras including the first class cameras up to the super-high class cameras by employment of different types of cameras. At present, the monthly production of cameras of one type in the individual makers is not so large, amounting to several tens of thousands of cameras at most. Consequently, the number of integrated circuit units of one type necessary for use in certain types of cameras is not large. Thus it is difficult to reduce the production cost by mass production thereof. This is one factor in the high cost of the camera. The provision of the corresponding number of types of integrated circuit units to that of types of cameras which are to be produced in the individual camera makers is disadvantageous not only for the service department of the maker, because it has always to keep sufficient quantities of all the types of integrated circuit units in stock, but also for repairmen, because the service is timeconsuming and requires considerably detailed knowledges from them. Therefore, therefore, when the automatic exposure control systems are designed to have different types of integrated circuit units with different types of cameras, individual camera makers find it very difficult to establish smooth progress from the development of new types of cameras through the design to the manufacture along with smooth marketing routes for the products. This results in an increase in the cost of the individual cameras. Further, this problem becomes serious in the production and service of super-high class cameras which represent a relatively small percentage of the total camera production.